Pyrite FeS₂

6–6.5

5.0

Metallic

Greenish black

Light yellow

Harder than chalcopyrite; called “fool's gold,” but harder than gold and very brittle

Magnetite Fe₃O₄

6

5.2

Metallic

Black

Iron black

Very magnetic; important iron ore; some varieties known as “lodestone”

Hematite Fe₂O₃

5.5–6.5

4.9–5.3

Metallic or earthy

Red or reddish brown

Reddish brown to black; also steel gray crystals

Most important ore of iron; known as “red ocher;” often used as red pigment in paint

Chalcopyrite CuFeS₂

3.5–4

4.1–4.3

Metallic

Greenish black

Golden yellow, often tarnished

Most important copper ore; softer than pyrite and more yellow; more brittle than gold

Copper Cu

2.5–3

8.96

Metallic

Copper red

Copper red to black

Can be pounded into various shapes and drawn into wires; used in making electrical wires, coins, pipes

Gold Au

2.5–3

19.3

Metallic

Yellow

Rich yellow

Can be pounded into various shapes and drawn into wires; does not tarnish; used in jewelry, coins, dental fillings

Silver Ag

2.5–3

10.5

Metallic

Silver to light gray

Silver white, tarnishes to black

Can be pounded into various shapes and drawn into wires; used in jewelry, coins, electrical wire

Galena PbS

2.5

7.4–7.6

Metallic

Lead gray

Lead gray

Main ore of lead; used in shields against radiation

Graphite C

1–2

2.3

Metallic to dull

Black

Black

Feels greasy; very soft; used as pencil “lead” and as a lubricant

Garnet
[Ca,Mg,Fe]₃
[Al,Fe,Cr]₂(SiO₄)₃

7–7.5

3.5–4.3

Glassy to resinous

White, light brown

Red, brown, black, green

A group of minerals used in jewelry, as a birthstone, and as an abrasive

Olivine
[Mg,Fe]₂SiO₄

6.5–7

3.3–3.4

Glassy

White or gray

Olive green

Found in igneous rocks; sometimes used as a gem

Hornblende
NaCa₂[Mg,Fe,Al]₅
[Si,Al]₈O₂₂(OH)₂

5–6

3.0–3.4

Glassy, silky

White to gray

Dark green to brown, black

Found in igneous and metamorphic rocks

Biotite
K[Mg,Fe]₃
AlSiO₁₀(OH)₂

2.5–3

2.8–3.4

Glassy or pearly

White to gray

Dark green, brown, or black

A type of mica, sometimes used as a lubricant